class Cat(object):
    def say(self):
        print("i am cat")


class Dog(object):
    def say(self):
        print("i am dog")


class Duck(object):
    def say(self):
        print("i am duck")


# 把定义的类放进list
animal_list = [Cat, Dog, Duck]
for item in animal_list:
    item.say(animal_list)

a = ["1", "2", "3"]
name_set = set()
name_set.add("4")
name_set.add("5")

# a.append(name_set)
# print(a)

a.extend(name_set)
print(a)
